'Unrealistic' experimental designs obscured effects of nitrogen pollution: Study

'Unrealistic' experimental designs obscured effects of nitrogen pollution: Study
© Richard Sexton; The Historic New Orleans Collection. (Image courtesy of The Historic New Orleans Collection)

Flaws in the design of experiments studying the effects of nitrogen pollution have obscured its true impact, according to research published Wednesday by the University of Exeter.

In the study, published in the journal Science of the Total Environment, researchers found past experiments have relied on models with far greater proportions of nitrogen deposits than the actual global average rate. Numerous species of flora and fauna, they wrote, are sensitive to nitrogen at levels far lower than those modeled in the experiments in question. As a result, he said, they can often respond to increased nitrogen levels in “subtle and non-linear” ways that the nitrogen-heavy, one-size-fits-all models will not necessarily reflect.

Nitrogen levels vary widely worldwide, with higher levels found in forests and heavily industrialized areas of Europe and Asia than the global average. The levels typically used in the experiments in question, meanwhile, are more characteristic of agriculture use of mineral fertilizer, the researchers wrote.

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"Despite decades of research, past experiments can tell us little about how the biosphere has responded to anthropogenic nitrogen deposition. A new approach is required to improve our understanding of this important phenomenon,” Dan Bebber of the University of Exeter, the lead researcher on the study, said in a statement.

The high levels of nitrogen used in the models, he added, would be more appropriate for research on topics such as the impact of agricultural fertilizers.

Future research, Bebber said, should properly account for different nitrogen levels in different regions and ecosystems and monitor nitrogen effects for longer periods. He also recommended further studies to properly analyze any correlation between environmental conditions and nitrogen concentration.

"Understanding the impacts of anthropogenic nitrogen has been a major goal of global change research, through observational and experimental studies,” he concluded. “However, there remains a wide gulf between global nitrogen deposition rates, and the experimental treatments applied to simulate them.”